The present invention relates to an ink dot printer including a means for storing magnetic ink; a pair of magnetic pole plates arranged opposite to each other to form a slit whose one end is immersed in magnetic ink supplied from the magnetic ink storing means; and a magnetism generating means for magnetizing the pair of magnetic pole plates to introduce magnetic ink supplied from the magnetic ink storing means into the slit and form a magnetic ink film in the slit. A plurality of needles are arranged adjacent to one another along the longitudinal direction of the slit and are each freely movable in the longitudinal direction of the needle between a first position where one needle end portion is immersed in the magnetic ink film in the slit formed by the paired magnetic plates and a second position where the one needle end portion is projected from the magnetic ink film in the slit. Driving means selectively drives the needles to move from the first position to the second position, wherein the one or more needles selected force magnetic ink, which has been stuck on the end faces of the one needle end portions at the first position, onto a recording paper at the second position to form dots of magnetic ink on the recording paper. Symbols such as characters or numerals are printed on the recording paper by the grouping of these dots.
A wire dot printer or thermal printer is normally used as a ink dot printer. The wire dot printer selectively drives needles whose tips directly strike a pressure-sensitive manifold paper on a platen or whose tips indirectly strike a recording paper on the platen through an ink ribbon interposed between the tips of the needles and the recording paper. In this fashion, dots are formed on the pressure-sensitive manifold paper or recording paper to print symbols, such as characters or numerals, by the grouping of these dots. In this conventional wire dot printer, however, a large amount of noise is caused when the symbols are printed onto the pressure-sensitive manifold paper or recording paper. In addition, no other paper except for the pressure-sensitive manifold paper can be used. Further, the expensive ink ribbon of the latter method must be changed frequently. The expensive ink ribbon also must be used in the thermal printer.
In order to eliminate the drawbacks of the conventional wire dot printer or thermal printer, there have been proposed various kinds of ink dot printers wherein magnetic ink is stuck on the end faces of the front end portions of the needles and wherein these needles are driven selectively to transfer the magnetic ink onto the recording paper to form dots thereon.
In the case of the conventional wire dot and thermal printers as described above, the density of dots formed on the recording paper is uniform, thereby keeping densities of printed symbols, such as characters and numerals, uniform.